Explanation:

- Primary healthcare: This is the first level of contact for individuals with the health system. It includes essential health services like immunizations, family planning, and basic care for injuries.

- Secondary healthcare: This represents a second tier of care within hospitals. It involves specialized consultations and expertise, like that provided by a dermatologist or a cardiologist.

- Tertiary healthcare: This is the most advanced level of care which includes specialized consultative care, usually on referral, and involves advanced medical investigation and treatment such as complex surgeries.

- All of the above: This option accurately combines all three levels, representing a comprehensive understanding of the health system.